1. Field of the Invention
The invention relates to an apparatus for direct shear stress testing of a sample.
2. Description of the Related Art
Asphalt mixture can be applied in various fields, including road systems, airport runways, railway engineering, architecture engineering, and the like.
FIG. 1 illustrates a conventional asphalt pavement 1, which is made by blending asphalt cement as a binding material with various granular aggregate and fillers in a suitable proportion to produce asphalt mixture, and subsequently paving the asphalt mixture on a subgrade (A) in a laminar construction that includes a subbase course (B), a base course (C), a surface course (D), and a friction course (E). Each layer of the laminar construction has its own specific function. For example, the friction course (E) is the upper layer of the asphalt pavement 1, and is used to resist the friction imposed by wheels of vehicles, and to increase the friction between the asphalt pavement 1 and the wheels so as to enhance braking capability of vehicles. The subbase course (B) is used to transfer the load (w) imposed through vehicle wheels to the subgrade (A).
When the asphalt pavement 1 bears the load (W) imposed through one of the wheels of the vehicle, deformation of the asphalt pavement 1 will occur. Referring to FIG. 2, the asphalt pavement 1 is subjected to compressive force (P) at the upper part thereof, and to tensile force (T) at the lower part thereof simultaneously. Referring to FIG. 3, the asphalt pavement 1 also suffers from shear force (S) in a substantially transverse direction, which can result in breakage of the asphalt pavement 1.
In view of the aforesaid, in addition to the load (W), the asphalt pavement 1 is also subjected to compressive force (P), tensile force (T), and shear force (S) that result from kneading and impact of the vehicle wheels on the asphalt pavement 1. Therefore, it is a requirement for the asphalt pavement 1 to possess sufficient strength to bear various stress.
FIG. 4 illustrates a conventional shear box 2 for testing shear stress of a soil sample 20. The shear box 2 includes two cylindrical caps 22,24. The cylindrical caps 22,24 are mounted on opposite end portions of the soil sample 20, which is cylindrical in shape, and are held by a holding device (not shown). The maximum shear stress of the soil sample 20 can be detected by applying two opposite force (F) onto the cylindrical caps 22, 24 in a radial direction until the soil sample 20 breaks.
It is noted that the shear box 2 is merely used for detecting the shear stress of the soil sample 20, which has a relatively small bonding stress as compared to asphalt mixture. Therefore, the requirements for the conventional shear box 2 are not sufficient for shear stress testing of an asphalt mixture sample.
Therefore, it is an object of the present invention to provide an apparatus for direct shear stress testing of a sample, such as asphalt mixture, which has a relatively high strength, which is relatively stable when holding the sample, and which is easy to assemble and disassemble.
The apparatus according to this invention is adapted to be mounted on a worktable of a multi-functional compression machine for direct shear stress testing of a sample. The apparatus includes a base plate, a supporting member, a fixing member, and a sliding member. The base plate is adapted to be mounted on the worktable of the multi-functional compression machine. The supporting member is mounted on the base plate, and includes a supporting plate vertical to the base plate. The supporting plate has a supporting face. The fixing member includes a first fixing unit mounted on the base plate. The first fixing unit has a stationary shear plate which includes a first shear face parallel to and facing toward the supporting face of the supporting plate. The stationary shear plate further has a first receiving hole formed transversely through the first shear face. The sliding member includes a sliding unit which has a movable shear plate interposed between and in sliding contact with the supporting plate and the stationary shear plate. The movable shear plate has a second shear face in contact with the first shear face and a second receiving hole penetrating transversely through the second shear face.
The movable shear plate is slidable relative to the stationary shear plate to align the first and second receiving holes so as to receive the sample therein, and to misalign the first and second receiving holes so as to cause the sample to yield.